Performance of many existing wireless systems, such as telecommunication systems or cellular radio communication systems, may be limited by interference from different radio devices, such as radio base stations. To combat effects of this interference, several so called interference mitigation techniques have been proposed.
According to some interference mitigation techniques, the interference mitigation is achieved though receiver design. Receiver design refers to design of a receiver comprised in a user equipment. Such a receiver uses for example interference rejection combining (IRC), successive interference cancellation (SIC) or the like to mitigate interference in a signal received by the receiver.
According to some other interference mitigation techniques, the interference mitigation is performed though radio resource management (RRM). Known RRM schemes for interference mitigation include for example different inter-cell interference coordination (ICIC) scheduling algorithms, employing fractional frequency division and appropriate power control mechanisms.
It should be noted that interference mitigation through receiver design is typically independent whether uplink or downlink is considered. The downlink refers to a signal received by the user equipment and the uplink refers to a signal transmitted by the user equipment. However, the ICIC scheme is different in downlink as compared to uplink, because in the downlink the interference originates from surrounding base stations, whereas in the uplink the interference originates from other surrounding user equipments, i.e. relative locations of user equipments in uplink affects the ICIC scheme resulting in higher other cell interference variance.
A known RRM scheme for interference mitigation, or interference management, is soft frequency reuse. In FIG. 1, a block diagram illustrating soft frequency reuse is shown. According to soft frequency reuse, a base station divides an available scheduling bandwidth, i.e. a certain frequency range, into two or more, not necessarily equal, portions. See portions CB11, CB12, CB21 and CB22 in FIG. 1. For example, a cell-edge portion CB11 of the scheduling bandwidth for a first cell C1 is defined and allocated to cell-edge users and similarly a cell-center portion CB12 of the scheduling bandwidth for the first cell C1 is defined and is allocated to cell-center users. Similarly, a further cell-edge portion CB21 and a further cell-center portion CB22 of the scheduling bandwidth for a second cell C2 are defined. The base station schedules its so called cell-edge users on the cell-edge portion CB11. The cell-edge users are typically located close to, or in the vicinity of, a cell border of the first cell operated by the base station. Thus, the base station transmits at a higher transmit power to ensure proper reception by such cell-edge users, i.e. user equipments at the cell edge. The base station schedules its cell-center users on the cell-center portion CB2. Thus, the base station can transmit at a lower power compared to the higher transmit power for the user equipments at the cell-edge. In order to mitigate interference towards the cell-edge users, the cell-edge portions CB11, CB21 are selected to be non-overlapping in terms of frequency for the first and second cells C1, C2, which typically are neighboring cells. In this manner, interference from transmissions of the second cell C2, towards a cell-edge user, camping on the first cell C1, will be mitigated. The second cell may be operated by the base station or by a neighboring base station. As a result, performance in terms of for example throughput will increase for the cell-edge user of cell C1.
A known Long Term Evolution (LTE) system comprises a base station, such as an eNB, utilizing soft frequency reuse. A first and a second user equipment are served by the base station. The first user equipment comprises an advanced receiver employing IRC or SIC. The second user equipment comprises a receiver without IRC or SIC. Hence, the LTE system comprises user equipments whose receivers are different in terms of interference mitigation. This may cause ambiguity in the network, i.e. in the LTE system.